Microwave oven door latch

ABSTRACT

An electrically actuated arrangement for securing the door of a microwave oven apparatus while the energy is radiating within the enclosure. The door can only be opened by the user after the heating source has been de-energized. Mechanical latching structures are eliminated and the novel door latch is adaptable to either the side-mounted swinging oven door as well as the drop down model.

United States Patent 1 Blackburn 1 May 15,1973

' 22 Filed:

[54] MICROWAVE OVEN DOOR LATCH [75] Inventor;

[73] Assignee: Amana Refrigeration, 1nc., Amana,

Iowa

Sept. 7, 1971 [21] Appl. No.: 178,044

Louis W. Blackburn,'Norway, Iowa [52] US. Cl. ..219/l0.55, 292/129, 292/201, 292/254 X [51 Int. Cl. ..H05b 9/06 [58] Field of Search ..219/10.55; 292/201 292/144, 129, 254

[56] References Cited UNITED STATES PATENTS 3,196,242 7/1965 De Vries et a1 .a ..219/l0.55

2,754,144 7/1956 Timms et al ..292/20l 2,543,214 2/1951 Wildberg ..292/20l UX 2,936,892 5/1960 McNeil et a1.

3,480,753 11/1969 Wilson et a1 ..2l9/l0.55

Primary ExaminerJ. V. Truhe Assistant Examiner-Hugh D. Jaeger Attorney-1-larold A. Murphy et a1.

[57] ABSTRACT An electrically actuated arrangement for securing the door of a microwave oven apparatus while the energy is radiating within the enclosure. The door can only be opened by the user after the heating source has been de-energized. Mechanical latching structures are eliminated and the novel door latch is adaptable to either the side-mounted swinging oven door as well as the drop down model.

5 Claims, 6 Drawing Figures PATENTEUHAY 1 5127s SHEET 1 OF 3 PATENTED RAY I 51973 SHEET 2 BF 3 PRIOR ART LATCH LOCK MICROWAVE OVEN DOOR LATCH BACKGROUND OF THE INVENTION This invention relates to microwave oven heating apparatus and means for locking the door of the heating enclosure once the energy source is energized.

Microwave ovens have found wide acceptance in the home market for the preparation of a wide variety of foods in extremely fast cooking times. Such apparatus has also found acceptance in the vending machines where complete meals can be prepared in a very short time. An energy generator for radiating microwaves within the oven enclosure is the magnetron oscillator used in World War II radar systems. Conventionally, such oven apparatus operates at assigned frequencies of 915 to 2450 Megahertz as determined by the FCC regulatory agency. The term microwave as used in the specification is defined as electromagnetic energy radiation in that portion of the spectrum having wavelengths in the order of approximately 1 meter to one millimeter in frequencies in excess of 300 Megahertz.

In view of the short time periods for the cooking cycle, it is desirable that once cooking commences the oven door be maintained in the closed position. This feature is particularly desirable in the vending machine applications where interruption of the time cycle can result in improper preparation of the food product. A door locking arrangement is also desirable to render the microwave oven apparatus completely safe, particularly when used by an inexperienced operator or, accidentally, by small children.

Present day microwave ovens have been adapted with a mechanical latching arrangement which must be slid into a locked position before the energy can be radiated within the oven enclosure. Such locking arrangements are manipulated externally by the operator when desired. The problems inherent with such external manipulation can be foreseen which gives rise to the need for a foolproof, fail-safe door locking arrangement for any type of oven door which is automatically operated in a safe and reliable manner to assure that the oven door remains closed while the energy source is operative.

SUMMARY OF THE INVENTION In accordance with the teachings of the present invention, an electrically actuated oven door latch is provided having means for engaging the lever arm ofa latch interlock switch. Conventionally, a door interlock switch is coupled in series with the latch interlock and is adapted to operate in conjunction with the movement of the oven door hinge. Both interlock switches must be in the closed position in order for the energy generator to operate. The latching arrangement is positively locked by spring lever bar means which are directly engaged by a solenoid operated movable pawl arrangement in a sweeping movement to lock the latch after the interlock switch lever bar has been depressed and thereby prevent opening of the door while the energy generator is operative. The circuit for the energizing of the electromagnetically controlled solenoid means includes the inner connection of the oven start switch together with the door interlocks. The unlocking of the disclosed door latching arrangements results only upon the de-energizing of the microwave generator. Several alternative positions for the solenoid actuated engaging means are disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS Details of illustrative embodiments of the invention will be readily understood after consideration of the following description and reference to the accompanying drawings, wherein:

FIG. 1 is an enlarged perspective view of the electrically actuated door latch arrangement embodying the present invention;

FIG. 2 is an enlarged perspective view of an alternative embodiment of the present invention;

FIG. 3 is a perspective view of a microwave oven apparatus with a drop down door and prior art mechanical lock;

FIG. 4 is a perspective view of the prior art mechanical locking structure as viewed from behind the control panel of the apparatus looking outwardly with the lock in the closed position;

FIG. 5 is a perspective view of a microwave oven apparatus having a side-hinged door arrangement; and

FIG. 6 is a schematic circuit diagram of an exemplary microwave oven apparatus utilizing the embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Before proceeding to a description of the specific details of the embodiment of the invention the applicable microwave oven apparatus as well as a prior art locking arrangement will be discussed. In FIG. 3 the microwave oven apparatus 10 comprises a hollow oven heating enclosure 12 defined by conductive walls 14. Casing 16 surrounds the oven enclosure as well as the high voltage electrical circuit means and oven controls. Access to the interior of the enclosure 12 is provided by means of an opening 18 suitably closed by a metallic door assembly 20. In this embodiment a bottom hinge 22 is provided and the upward and downward movement of the door is controlled by a pair of spring tension counter balanced arms 24 together with a handle (not shown). The arms 24 contact door interlock switch means having a lever actuating arm which are housed adjacent to walls 14 and have not been illustrated for the sake of clarity.

The door assembly 20 in this embodiment is shown as beingrecessed so as to be flushed-mounted. The

door comprises a panel member 26 having a plurality of perforations 28 which aid in the prevention of the escape of any electromagnetic energy radiation during operation of the oven apparatus. Ring member 30 is joined to panel member 26 with the overall door assembly having a stepped configuration and wall 30a contacts wall 32 of the surrounding access opening 18 when the door is in closed position. A hook-type latch 34 is pivotally mounted on ring member 30 and is supported by wall portion 30a. A mating slot 36 in wall 32 is adapted to receive latch 34 when the door 20 is in the closed position.

In accordance with prior art teachings a mechanical latch locking arrangement 38 is slidably disposed and supported by the escutcheon control panel 40. The latch lock is actuated by means of a slide control member 42 disposed within opening 44. Panel 40 also supports a 5-minute timer switch 46 as well as a 30-minute timer switch 48. Additionally, a start control button 50, stop control button 52 and light control button 54 are mounted on the panel 40. Referring now to FIG. 4 the reverse side of the panel member 40 is shown. Another slide member 56 to which the control 42 is affixed by screw means 58 provides for movement of bar lock member 60 which moves the tongue 62 to a position engaging the top of the latch 34 when it is positioned within the slot 36. With this mechanical locking arrangement the operator must manually slide the assembly to the latch-locking position before starting of the operation of the apparatus as well as after completion of the cooking cycle.

FIG. illustrates a microwave oven apparatus 64 with an access opening 66 enclosed by means of a sidemounted door assembly 68 having a pivotally disposed latch member 70. In this arrangement control panel 72 supports a mechanical latch lock 74 which slidably moves a bar member 74 to engage slot 76 in sidewall 78 ofthe door assembly. In this embodiment the latch interlock switch is supported by plate 80 shown mounted to a casing wall 82. Inner wall 86 defines the oven enclosure.

Referring to FIGS. 1 and 2 the embodiment of the invention will now be described. The side-hinged embodiment will be described with the components supported by plate 80 joined to casing wall 82. Door assembly 68 is recessed and closes the opening 66 with the latch 70 supported by means of a pivot 84 extending through sidewall 78. A bezel member 88 frames the wall portions of casing 82 adjacent the door assembly 68. Interlock switch 90 is provided with an operating lever arm 92. Upon the introduction of latch 70 within the slot 94 in wall 96, the lever arm 92 is depressed by the hook portion 98 to actuate this component of the main circuit which in combination with other interlock means operates the energy generator. Associated with such arm means are spring biased contacts or the like which are well known in the art and need not be described in detail in this specification. What is relevant is the fact that until all the interlock switches are closed by suitable movement of their respective operating arm levers no energy will be radiated within the cooking enclosure. The lever arm 92 is of a resilient material so that it is biased away from the switch 90 in the open position.

An electromagnetically actuated solenoid member 100 is provided with a reciprocally movable arm 102 supporting adjacent to its outer end a pawl member 104 which is pivoted by rod 106 extending from bracket 108. Linkage 110 adjacent to the end of arm 102 translates the reciprocal movement into what may be referred to as a sweeping motion of pawl member 104 to engage a resilient member 112. The engaging portion of member 112 is provided with a substantially V-shaped portion 112a which engages the top of latch hook portion 98. The latch member 70 is urged downwardly to the locked position by the resilient member 112 and the hooked portion 98 engages a bracket member 1 14 supported adjacent to the inner side of the slot opening 94. The solenoid member 100 in the energized position with the pawl member 104 disposed vertically will lock the latch member 70 in contact with the bracket 1 14. The reverse thrust of the arm 102 will result in the pawl member being removed from the vertical position in the direction indicated by the arrow 116. The blocking feature of the pawl member on the spring member 112 is thereby removed and the door may be opened with the latch member 70 clearing the end of the bracket to provide for easy opening of the door.

While no internal stop means have been provided for the de-energized end of the solenoid position it may be desirable in certain structures to provide such a structure to limit the end of reciprocal movement of the pawl member 104. Upon energizing of the appropriate circuits to be hereinafter described, the electromagnetic solenoid will again be energized and pull arm 102 inwardly to again urge the pawl member 104 to be in the locked position.

FIG. 2 illustrates an alternative embodiment of the invention wherein pawl motion is now provided in a horizontal direction rotated approximately 90 from the vertical position indicated in FIG. 1. In this description, like structure has been similarly numbered to assist in the explanation of the invention. Pawl member 118 is now actuated by arm 120 in a reciprocating direction indicated by arrow 122. The upper portion of resilient spring member 112 is thereby contacted by the flat portion of the pawl member 118 rather than the end of the portion shown in FIG. 1. A more positive engagement in the locked position may thereby result. In this embodiment the pivot member 124 extends in a vertical position oriented transversely from the position of pivot member 106 in FIG. 1. It will be evident, therefore, that the within disclosed electrical door latch locking arrangement provides for automatic control with secure locking of the door without extra operator manipulation being required.

Referring now to FIG. 6 an exemplary schematic circuit diagram is illustrated. The magnetron energy generator 126 has been illustrated as being for the permanent magnet type and, therefore, no circuitry for an electromagnet has been disclosed. If such a magnet'is desired appropriate adaptation in the manner well known in the art will be required in the high voltage circuit. A conventional three terminal connector 128 having a grounded lead 130 provides for the connection of the circuit to the customary house line voltages which can be 1 l5-l20 Volts or 220 Volts AC. Terminal board 132 provides for a connection of all the components to the line voltages. Light switch 134 actuated by button 54 mounted on panel 40 controls the oven light 136. The door interlock switch 138 which is controlled by the movement of the door counterbalance arm in,

the drop-down model is connected by start-stop switch 140 actuated by panel buttons 50 and 52. A stirrer of any well known configuration in the art providing for the distribution of the energy within the enclosure is actuated by means of motor 142. A fan 144 is also provided to cool the magnetron energy generator as well as the high voltage components including the DC rectifier circuit 146 and step-up transformer 148 having the conventional primary and secondary windings. The latch interlock switch denoted by the numeral 90 in FIGS. 1 and 2 is coupled in the circuit to a thermal cutout switch 150 to provide further safety features. The 5-minute timer motor 152 is controlled by means switch 154 actuated by knob 46 in panel member 40. A dial light 156 is also provided for in the timer arrangement. The 30-minute timer motor 158 is actuated by switch 160 controlled by means of knob 48 previously described. Dial light 162 is also provided for in the circuit to assist in the reading of this timer and indication of energy radiating in the oven.

Electromagnetic solenoid 100 is connected in the cir' cuit by lead 164 leading from the timer motor arrangement and is coupled in series by lead 166 with the startstop switch 140. In this arrangement the latch interlock switch arrangement 90 is coupled in series with the solenoid 100 when the interlock is depressed. It will also be noted that door interlock switch 138 is also arranged in series with the switch 90 via the terminal board 132. In this manner both interlock switches are actuated upon the closing of the door and with the start-stop switch 140 actuated the latch is automatically locked to prevent further opening of the door while the energy generator is operative.

The high frequency energy generator comprising a magnetron oscillator 126 is coupled by means of high voltage transformer and DC rectifier circuits in series with the door and latch interlock switches as well as the start-stop switch. The generator includes a cathode 168 together with a grounded anode 170. A plurality of cavity resonators 172 are circumferentially disposed about the cathode 168. The microwaves are coupled to the oven cooking enclosure by means of a coupling loop or antenna 174 which is commonly disposed within a waveguide launching section. The DC rectifier circuit 146 may be of the full wave or half wave voltage doubler network type for energizing the magnetron generator 126.

An efficient and foolproof, as well as reliable, fully automatic door locking arrangement is disclosed which assures the completion of the cooking cycle as well as preventing tampering once the energy generator is operative. The arrangement is adaptable to any type of door mounting. The arrangement has an inherent long life feature in that wear and tear will not materially affect the electrical arrangement. Numerous variations, alterations or modifications of the disclosed apparatus will be evident to those skilled in the art. It is intended, therefore, that the foregoing description of the invention and the illustrative embodiments be considered in the broadest aspects and not in a limiting sense.

What is claimed is:

1. Microwave oven apparatus comprising:

an enclosure having an access opening;

a microwave energy generator adapted to radiate energy within said enclosure;

a door for closing said opening;

a latch member pivotally supported by said door;

interlock switch means connected in an electrical circuit for operating said generator including a lever arm;

said latch member being adapted to depress said lever arm when said door is closed;

a resilient member adapted to engage said latch member; and

an electromagnetically actuated reciprocally movable lock member adapted to engage the upper wall portion of said resilient member and prevent movement of said latch member while said generator is operative.

2. Apparatus as set forth in claim 1 wherein said door is hinged so as to be movable sideways when closed.

3. Apparatus as set forth in claim 1 wherein said door is hinged as to be moved upwardly when closed.

4. Apparatus as set forth in claim 1 wherein said reciprocating member includes mechanical linkage and a pawl at the outer end with said pawl adapted to move in a vertical plane when said lock member is actuated.

5. Apparatus as set forth in claim 1 wherein said reciprocating member includes mechanical linkage and a pawl at the outer end with said pawl adapted to move in a horizontal plane when said locking member is actuated. 

1. Microwave oven apparatus comprising: an enclosure having an access opening; a microwave energy generator adapted to radiate energy within said enclosure; a door for closing said opening; a latch member pivotally supported by said door; interlock switch means connected in an electrical circuit for operating said generator including a lever arm; said latch member being adapted to depress said lever arm when said door is closed; a resilient member adapted to engage said latch member; and an electromagnetically actuated reciprocally movable lock member adapted to engage the upper wall portion of said resilient member and prevent movement of said latch member while said generator is operative.
 2. Apparatus as set forth in claim 1 wherein said door is hinged so as to be movable sideways when closed.
 3. Apparatus as set forth in claim 1 wherein said door is hinged as to be moved upwardly when closed.
 4. Apparatus as set forth in claim 1 wherein said reciprocating member includes mechanical linkage and a pawl at the outer end with said pawl adapted to move in a vertical plane when said lock member is actuated.
 5. Apparatus as set forth in claim 1 wherein said reciprocating member includes mechanical linkage and a pawl at the outer end with said pawl adapted to move in a horizontal plane when said locking member is actuated. 